The Vanity Fair writer, Jim Windolf, wrote about learning of this news while visiting Spielberg at his Amblin Entertainment office on the Universal lot. The writer claims to have glanced at a table on which headshots of Will Smith, Taye Diggs, Adam Arkin and Kevin Spacey were visibly linked to the Chicago Seven project. None of the actors' proposed roles were determined, however. Now, I don't want to assume that Spielberg planted those headshots for Windolf to see, but it does seem strange that such a sometime-secretive filmmaker would let something like this be leaked in such a way. It also seems strange to think that anybody, even Spielberg, would need a headshot of Smith in order to decide to cast him as Black Panther (and 8th of the originally Chicago 8) Bobby Seale, who I will assume Smith's being considered to play. Windolf also claims that Sorkin's script is somehow based on the documentary Chicago 10, which premiered at Sundance last year and is being given a limited release next month. As Jessica noted the other day, you could probably make that a must-see primer while you await Spielberg's film (and more news about it). Another idea is to check out Steal this Movie (often available for free online), which is also good to watch for the appearance of a very young Michael Cera as Abbie Hoffman's son, America.